Instantaneous rate of change of a sphere

1. Mar 2, 2008

ivysmerlin

1. The problem statement, all variables and given/known data
Find the instantaneous rate of change of V with respect to r when r=5 micrometers

2. Relevant equations

V=4/3pi(r^3)

3. The attempt at a solution

would you just take the derivative? and if so, wouldn't it just be zero, because it comes out to be a real number, right? but that doesn't seem right...

2. Mar 2, 2008

dlgoff

What is the derivative of V=4/3pi(r^3)? Now what would the value be at r=5micrometers? Not zero.

3. Mar 2, 2008

ivysmerlin

ooh, im an idiot, thanks